Process for shaping plastic sheet material



Nov. 28, 1950 H. E. SMITH PROCESS FOR SHAPING PLASTIC SH EET MATERIALOriginal Filed June 1 1 2 Sheets-Sheet 1 INVENTOR.

HARRY 5. SMITH.

ATTOR NEYS H T M 2 n R W m 5 t 1 s a a m s E e 6 N N H m m K w E R 5 "w7/ 7 m m m 2 m 8 6 a m X M 4 m 4 H M m s .v r 1 m m M 2 1 1 w 4 m ML Y TY 2 B E 7 7 m S y, 9 L H C W 7 6 7 6 T H w M m S H 3 j H M a e m 6 6 1 RT m w A 5 m mm H Nov. 28, 1950 Original Filed June 19, 1945 PatentedNov. 28, 1950 v vIPROCESSEOR SHAPINGBLASTICSHEET l MATERIAL 5 De awa.Ori inal application l 347. in 'degil l -er e1 2 Claims.

"1 Thisi veetiop xelei s efi a hep s f ,Sheet terial, andlfilates moreparticiilarly to; the 9 1 nr eess o t e. shenine' Qf hlf eh st e mate iappli atio 600, 3

.11 a div si n f en seii n ed J1me l9, 1945 wherein the .Y t in eiitermo l i isclain ed.

-;.-W,, la h d esi turese his n enti n ma be employed forthe shaping ofsheets of plastic .sheetwmater al nt ,va o sio vms, it i ,pe 'iie le ieble tqi e t rlewi efih l Ce dies an i coyers therefor from plastic shetlm .er iakhaviwg bas 9f t rm la t lcprnpqun such. or-exam e, piteellul cellulose a eta e, cellulo e r i La "efil il l .buWn eethm c lluo e benz ls ,1 1 5 W911 semen-este Qf el ul m xe e te 9.1 9 1 c p e, syhe ic re in a d lme i 'a ionv ro n t .Ehis, vept om l erei r, wi lfh-fldscr bed n: .1 :mect.ion w l h d awing 19 low, cen ai e bod es rfiro thrm c she dm tsr el gblan s es tclommp lyie ae ed mth Plasi aindustr.thainemii etu Q h l ow eentai e i ies 01" Waters .i velves the u e q acd aw n di stru lti r umade re eta o ot e suitable c jat ial- ,T e,.die=tmptu. m r ses, a sui abl rsunpert tm m al l ddo n-n ate, asupportin Mas; wwhich is Xed a femaledie "ef i if 3 sire Q ..,n ,ess y,. alsuitabltautf embe me. ie nale die "and the ,,hold-,down plate are hea ed 1Wsuita le me ns" i hei drawi 9 gtmin l temp rature fo t aft c larltyp 9ftPlastic heme inr eess F he. force. m mh max-also beheated, but it isgenerally maintained a isi rl a v 39 m qm emtu c W u ere isio f r-hea gIf tl s desira le to. gis inate any lab rbed1h afi: m e mw P vide --I:-1 srine the temp t re e the, for e, m m e in corld rl m in uTheahlsi-dow m t p supported directly above the female die; c and is adaptedto 11016. rthe plastic sheet'niaterial against the yvorlging surface ofthe female T die n lenrbe with justsufiicient pressure topermit asrnqoth and unifprm drawing of said plastic :sheet by.,th e noyernentqf.the force into the felipa iemmedia l pr or t l e t e i "thaw stru ture e'i h ew n e t l t June 19, 1945, Serial No.

and this -e v icafi nl March (Cl. 18v-56) -2 thermoplastic sheetmaterial or blank is generallyfsiibjectedto a short period of preheatingcverthe entire area thereof in order to obtain adequatef'and iiniformplasticity for theparticular type of plastic beinjg'proce'ssed. Normallyseparate 'die structures "are employed for drawing the containerbody"anilthetelescopic cover for acompiete contamerz When drawing hollowplastic container bodies and covers in the foregoing conventionalmanner,iii ijclesi able 'a'iicl objectionable" quality characteristicsnanifestj themselves. Thepredo'xni'ri'at'ing' andj'most seriousobjection *is 'the presence of unsightly surface blemishes particularlyon the "sicle WaIL'and to some extent on the top and/0r bottomsiirfac'e'i of such bodies'oi' covers, 'whose end shape orcontourinvolves partly depressed; extended, stepped, concayi'e; convexor compound-curved 'surfacesl""l'fhe bIe'mishes are mostobjectionable'in'deepEdraWn tranS- parent bodies or covers, especiallywhen viewed by' traiismittedflight' thus causing more 'oi1ess lightrefraction, 'a ntl result"in the appearance of so called sma-1lmark-offsofi-isetsiihgs, heatrnarks, blistersfpits, pimples and, streaks.

Another object of this invention is the prolvifsio n 'of improvedprocess for the drawing of hollow thermoplastic container bodies" andcolvers 'en plc'yin'ghoth mechanical and fluid pressure.

LStill: another object of this invention is the proyision'cf a proces'sf or the draw ng of hollow thermoplastic container flcctiies and telscopic tower therefor from thejsafiie die."

further-object of this invention is the proision '0': a process for thedrawings: hollow Ltliern oplasti'c container bodies and telescopicepverstherefcr i In the same die, and at the same time, bythe ji se ofsuitable interchangeable end former elements, proclucing on th"closedengl surface of the container bodiesancljco'vers flat, concave, convex,pr compdfind-ciiriie effects w m aheran; v alinia ei s ff p t al la n,el s e t fiece i h e s ems, fiia elmerls er ,Iil insignia r (f om mynovel force member,

' Figure 3 is a vertical sectional view showing the structural detailsof the female die elements with a forming pad in position,

Figures 4, 5, 6 and '7 are vertical sectional views,

on an enlarged scale, of modifications of end formers, and

Figure 8 is a vertical cross-sectional .view of a cover formed by theuse of an end former.

Like reference numerals indicate like parts throughout'the several viewsof the drawings.

In its broadest aspect, this invention contemplates the shaping of athermoplastic blank, preheated differentially or locally, into closedend cylindrical bodies by means of a shaping press comprising a force ofnovel construction which is adapted to draw the blank from between blankcontacting surfaces of novel design into the female die opening in whicha former for contouring the closed end is carried.

Referring now to the drawings for a detailed description of thisinvention, and particularly to Figure 1, the reference numeral 9indicates a ram of a press, preferably of the type shown and describedin application S. No. 554,888 filed September20, 1944, now United StatesPatent No. 2,429,960. In fact, the present die structure insubstantially its entirety may be incorporated in the process of saidprior application. The ram 9 is provided with an opening I! forreceiving a projection l2 of a hollow force, or male die, generallyindicated by reference numeral i3, bolts i4 retaining the force on saidram.

The force l3 comprises a solid portion l5 of any suitablematerial havingan integral hollow portion It the free edge ll of which forms a forminglip. The outer surface of the hollow portion of the force I3 is cut awayto form a circumferential channel I8 for receiving a cylindrical cushionI9 which is about in thickness and preferably of very smooth, soft,resilient material such as rubber. A packing band 2! of a stiff fabriccoated with coarse abrasive is preferably employed between the rubbercushion I9 and the outer Wall of the force I 3. The rubber cushion I9 isfirmly supported in the channel it by being tautly stretched over thecoars abrasive surface of the packing band 2| and the cushion is made toconform accurately to the desired outside diameter by the insertion ofthin paper shims 22 between the inner surface of the packing band 2! andthe bottom of the channel H8.

The rubber cushion I9 is preferabl prepared as follows: A piece ofcommercial grade vulcanized soft rubber tubing of the desired length andhaving a /32" wall thickness is turned inside out and stretched tautover a suitable mandrel that is somewhat larger in diameter than thediameter of the channel l8. The uneven inside surface of the rubbertubing is ground to a uniform finish with a high speed Carborundumabrasive wheel, such as #100 grit, working along the length of thetubing while it is being rotated parallel with the face of the abrasivewheel. After draw. Accordingly, force member leveling the inside surfaceof the tubing, it is removed from the mandrel and is again mountedthereon with the smooth inside surface against the face of th mandrel.The rough and uneven outer surface of the tubing is then accuratelyground to a smooth finish wall-thickness of A A cushion prepared in thismanner prevents the contractive pressure of the heated plastic fromdeveloping objectionable surface blemishes on the inside surface of theside wall during the drawing of container bodies or covers. If desired,powdered talc or other soft lubricant may be applied to the outersurface of cushion 19 in order to protect th smooth surface thereof andto facilitate the removal of the drawn body or cover.

The force [3 is provided with fluid ducts 23 and 24, the purpose ofwhich will hereinafter be set forth. Stop cocks 25 are placed in theducts to control the flow of fluid therethrough.

Mounted on ram 9 is a plate 26 having a flanged central opening 27 forreceiving the end of said ram, the plate being held in position on saidram by means of bolts 28 passing through the flange 29. The plate 26 isalso provided with openings 3| for slidably receiving the upper ends ofsupport rods 32 to the lower ends of which is fixed a hold-down plate 33apertured at 34 to permit the passage therethrough of the'force l3.Expansible springs 35 are carried by the support rods 32 and aremaintained in position by means of collars 36 held on said support rodsbypins 31. The force l3 cooperates with die plate 38 of the female dieto form the plastic container bodies and covers therefor. Said die platewill be more fully described hereinafter. I

The design of force i3 differs in still another structural detail fromconventional practice in the dimensional relation of the maximumdiameter of the forming lip Ill, and the maximum diameter of thecylindrical cushion [9 at the point of the maximum depth of draw. Forexample, in drawing a container body such as shown by dotdash line 39 inFigure 1 from .020 cellulose ace-.- tate plastic, the maximum diameterof the forming lip is 3.028 and the diameter of the cylindrical cushion19 at the point of maximum point of draw 3.025 which results in anascending taper of the force member i3 that is equivalent tosubstantially 0.0015" in diameter per inch of [3 has an ascending taperwhereas conventional practice, for the purpose of easing the withdrawalof the force member, employs a descending taper of the force of at least0.0015" per inch of draw from the maximum point of draw to the lowerextremity of the force member or side wall. This ascending taper offorce member [3, shown more clearly in Figure 2, further minimizes thecontractive pressure of the heated plastic on the surface of thecylindrical cushion [9 which, in association with the amount ofclearance with the aperture 4| of die plate 38 and the diameter of theforce member [3 at the point of maximum depth of draw, together with thestructural details of the force member previously described, furtherinsures against the development of surface blemishes on the insidesurface of the plastic body or cover.

The die plate 38 has affixed thereto in any suit- .able manner, on thesurface or in an annular groove 32, a spacer ring 43 of such thicknessas to establish a space 64 of predetermined size between the upper orworking surface of the die plate 3S and the hold-down plate 33 (seeFigure 3). The downward travel of ram 9, guided by plate which may b ofabout #1 60 grifi revolving at high peq at right afigles to'ahdtvotkifigacross the rotating surfa'ties 0f aid p'IateS. This p'i'o'duces"circular Sufi-ace" strdtures om'pbsed' of a multitude "of theheatewplastic must 1 initially contact a and from between which *surfaces itieasily and u'ni= 13111561 I i of'the'idie zplat'e-fifisc; Following.the :circular grinding. operation; the; working, surfaces of'ttheypiatesi may be -electrqrplated with a hard chmmium finishgwhiehstill jurther fae ilitates the movement of the heated plastic from thefixed space-A li and which also imparts a very hard and subs-tantiallyperma ent wear-free prof-1 teetivecoating to said working; surfaceseTheiichannelafl in die plate 38 is covered by an annular cover plate 5!fixed to the bottom-0f the die plate "by meansflf -screws;fl5 2 ;.The,.die plate is carried on a support 53;]outjis separatedtherw fr m; b ;r,,ans, O a n y a n k t 4 th s pp t, ."i u rine ig k t and di p a e be nlqw q ethe yJ, ew;h 1tsm.5 ap etsupno 53 is p ovqe m h 51 1 25. 56 a sca ried on the m tanequ lyw hthe fio m t on 9 h conr. H z e rmd rn vea,t e e oses en r of may be given a multiggoneave and/or an embossed Lerati w; s n ace er: m t hanic l y o by uiql p e s reggre 1, means gsshownior mechanical ly e; entaine .b dY-..1. ia mea s n mnr a forggne Ipacl ifl si ae: mca e u fas e 1,1 h close end; of Q;rthaaslesimslyeentouz suitably 5. s ai'l angem d su 1 t; le ine l e eove Figure 4 shqws" in Figure 4 may also be employed Hdwejver, n o1 inthis former is employed for the production of I a multi-convex closedend contoured gloss finish cover whose central area embodies an embosseddecoration. A cover shaped and embossed substantially like a coverproduced with the end former of Figure 5 is shown in cross-section inFigure 8. With the end former shown in Figure 5, the same method ofprocedure is followed as that employed in connection with Figure 4except that for the purpose of establishing the proper degree ofconvexity a fixed vertical dimension of suitable degree is maintainedbetween the face of the embossing element 11 and the upper face of theformer pad I l, and the heating element 18 is so adjusted as toestablish the desired temperature, i. e. a temperature of about 290 F.,in the embossing element.

In Figure 6, there is shown an assembled end former which is fitted witha fiat-top brass embossing element '19, the entire face of whichembodies an engine-turned decoration, while Figure 7 shows an assembledformer fitted with an open center brass embossing element 8! producingyet another decorative effect on the closed end.

Itis important that the plastic blank employed in the drawing or formingoperation be properly preheated before the same is placed in positionwithin spacer ring 43 on die plate 38. Proper temperature conditions areestablished on the plastic blank by differentially or locally heatingthe same. To obtain the most satisfactory surface quality in thecompleted container body, a sufficiently high temperature, and thus ahigh degree of plasticity, is given to such areas of the blank wheremaximum stress is developed during the forming operation, and asubstantially lower temperature is given the plastic blank to such areaswhere a minimum of stress is developed. Thus in drawing a containerbody, the outer circumferential area of the plastic blank, where itcomprises plastic material having a basis of cellulose acetate and has athickness of .020", is given a temperature of about 280 F., by suitablepreheating means (not shown), for the satisfactory deep draw of the sidewall, while the central area of the plastic blank which forms theconcaved closed end and where the minimum stress is developed ispreheated to about 150 F. It is to be understood, however, that thetemperature conditions and the areas of the blank which aredifferentially heated will depend upon the nature and thickness of theplastic material employed and the type of container body or cover beingformed. It may be necessary or desirable to differentially or locallyheat the plastic blank to produce three or more areas each having adifferent temperature and therefore, a different degree of plasticity.

Following the differential heating of the plas tic blank, it is quicklytransferred to the working surface of die plate 38. The ram 9 is thenimmediately lowered bringing down the holddown plate 33, properlycentered by guide rods 45, until it comes into contact with spacer ring.43. The continued downward travel of the ram plate and is so strippedfrom the force.

brings increasing pressure to bear on the springs 35 by plate 26pressing on collars 36 until the hold-down plate is'rigidly held againstthe upper surface of spacer ring. 7

Further downward travel of the ram carries the hollow portion N5 offorce [3 into the aperture '34 of the hold-down plate and brings theforming lip I! of the force into contact with the upper surface of thepreheated plastic blank. As the downward travel of the ram continues,the force draws the plastic blank from between the working surfaces ofthe hold-down plate and die plate into the forming aperture M of the dieplate. The drawing of the plastic blank from between the workingsurfaces of the hold-down plate and the die plate is continued, thusforming a cylindrical shape closely fitting completely around thecylindrical rubber cushion I9 on the force extending from the forminglip I! to the maximum depth of draw which is located slightly below theupper end of the rubber cushion.

At'a point slightly less than the maximum depth of draw, the centralarea of the outer surface of the closed end of the now cylindrical bodyis pressed against the former pad 59. The continued downward travel ofthe ram to the maximum depth of draw further presses the closed end ofthe cylindrical body against the former pad until the outer periphery ofthe closed end is pressed between the forming lip l1 and the outerperiphery of the former pad, thereby producing in the closed end amulti-concave contour.

On raising the ram, the cylindrical body formed is carried upwardly onthe force until the flange 82 on the cylindrical body comes into contactwith the edge of aperture 34 of the hold-down If desired, the flange 82may be removed from the cylindrical body in any convenient manner.

As will appear from the foregoing description, the die structure of theinstant invention is such that container bodies and telescopic coverstherefor may be made from the same die, continuously if the said diestructure is incorporated in the press of application S. No. 554,888,now Patent No. 2,429,960. The telescoping of the cover on the containerbody is effectively accomplished by beading the open ends thereof,preferably in the manner shown and described in my application S. No.600,346, filed June 19, 1945.

It is to be understood that the foregoing detailed description is givenmerely by way of illustration and that many variations may be madetherein without departing from the spirit of my invention.

Having described my invention, what I desire to secure by Letters Patentis:

1. In a process for shaping thermoplastic sheet material having a basisof cellulose acetate and a thickness of 0.020 inch into a deep-drawncylindrical body having a closed end, the steps of heating the outerperipheral area of said thermoplastic cellulose acetate sheet materialwhich, when deep-drawn forms the walls of said container, to atemperature of about 280 F. and the central portion, forming the closedend, to a temperature of about R, then deep-drawing the differentiallyheated cellulose acetate sheet through an aperture by applying a drawing force to the said cellulose acetate sheet only over an annular areaconcentric with said central'portion, and. after the cylindrical body is9 formed, shaping the closed end of said body by applying fluid pressurethereto.

2. In a process for shaping thermoplastic sheet material into adeep-drawn cylindrical body having a closed end, the steps ofdifferentially heating the thermoplastic sheet material prior to theshaping operation, drawing said differentially heated thermoplasticsheet material through an aperture by applying a drawing force to saidthermoplastic sheet material only over an annular area to form the wallsof said body, and, after the cylindrical body is formed, shaping theclosed end of said body by applying fluid pressure thereto.

HARRY E. SMITH.

10 REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number Name Date 2,120,328 Ferngren June 14, 19382,229,613 Strauch Jan. 21, 1941 2,255,117 Helmstaedter Sept. 9, 19412,270,187 Dulmage Jan. 13, 1942 2,425,390 Palmer et a1. Aug. 12, 1947

